SEATAC, Wash. (AP) — Federal crews said there has been a dramatic increase in violent conduct at airports and on planes. The Federal Aviation Administration said the dangerous behavior doubled in the past month. The FAA is investigating more than 2,500 cases of violence. At least 1,900 of those cases involved a dispute over masks. Flight crews are seeing fistfights and verbal and physical assaults of flight attendants. On Sunday, a Southwest Airlines flight attendant lost two teeth during an assault. In January, an Alaska Airlines passenger bound for Seattle shoved a flight attendant. That person is now facing a $15,000 fine.